1. Enabling Grids for E-sciencE www.eu-egee.org ISSGC’05 XML documents Richard Hopkins, National e-Science Centre, Edinburgh June 2005

2. Enabling Grids for E-sciencE ISSGC’05 – June 2005 XML 2 Overview Goals – –General appreciation of XML –Sufficient detail to understand WSDLs Structure –  Philosophy  Detailed XML Format  Namespaces

3. Enabling Grids for E-sciencE ISSGC’05 – June 2005 XML 3 A Markup Language XML = eXtensible Markup Language “Markup” means document is an intermixing of –Content – the actual information to be conveyed - payload –Markup – information about the content - MetaData 22/10/1946 … is markup – says that the content is a date –Self-describing document –date is part of a markup vocabulary –  a collection of keywords used to identify syntax and semantics of constructs in an XML document

4. Enabling Grids for E-sciencE ISSGC’05 – June 2005 XML 4 Extensibility XML = eXtensible Markup Language “Extensible” means the markup vocabulary is not fixed Compare with similar NON-extensible language –HTML (Hypertext Markup Language) –Fixed markup vocabulary e.g This is a paragraph. I like it. This is another paragraph –A presentation language for describing how a document should be presented for human consumption – This is a paragraph. I like it. This is another paragraph –For HTML the language is fixed and implicit in the fact that this is an HTML document – single-language document XML requires explicit definition of the language One document can combine multiple languages

5. Enabling Grids for E-sciencE ISSGC’05 – June 2005 XML 5 Multi-lingual Documents businessForms:Invoice –An Invoice construct within the businessForms language BusinessForms (mythical) –A language defining structure of business documents –For business interoperability –Doesn’t prescribe the language of individual items such as dates  Taken from separate languages - USnotations:date Language names are actually universally unique URIs – www.DesperatelyTryingToStandardise.org/BusinessForms - see later 10/22/2004 123-768-252 17.53

6. Enabling Grids for E-sciencE ISSGC’05 – June 2005 XML 6 Multilingual Pros & Cons Separation of concerns – Design Factoring –Design of purchase order structure and date format etc are independent concerns –Re-use of language definitions, e.g. date formats in many languages –Extensibility – Purchase order accommodates new product identification schemes (e.g. ISBN for book stores) Of course, only works if both ends “understand” all languages used Makes things more complex – –Creating and identifying the languages 10/22/2004 123-768-252 17.53

7. Enabling Grids for E-sciencE ISSGC’05 – June 2005 XML 7 Types of XML Language Fundamental Standards –E.g. SOAP - the language for soap messages  soap-envelope:header soap-envelope:body  A soap message is an XML document and its parts are identified using this vocabulary –Goal is a factoring that gives pick-and-mix of combinable standards –Associated with any WS standard will be a Schema definition of its XML language …. Community conventions –Perhaps, our BusinessForms language Specialised Data Structure –Java configuration tables …. Specific Application Language –myProgram:parameter1 –The language used in invoking particular operations of a web service

8. Enabling Grids for E-sciencE ISSGC’05 – June 2005 XML 8 Human & Machine Oriented Human readable –Sort of - OK with decent editor –Is de-buggable –Important for meta-data documents,  E.g. WSDL Machine processable Self description enables –General tools for producing and consuming XML documents Verbose –OK except for large data –Messages may have attachments not in XML How it really looks 10/22/2004 123-768-252 17.53

9. Enabling Grids for E-sciencE ISSGC’05 – June 2005 XML 9 XML – DETAILED FORMAT Structure  Philosophy  Detailed XML Format  Namespaces

10. Enabling Grids for E-sciencE ISSGC’05 – June 2005 XML 10 Document Structure Main structure of document is Prolog – like headers; usualy standard and un-interesting Element – the actual document – recursively has nested elements –Immediately following the prolog Miscellaneous – –white space and “supplementals” allowed throughout with some restrictions –Supplemental – a Comment a Processing Instruction (PI) … prolog Root element PI Comment

11. Enabling Grids for E-sciencE ISSGC’05 – June 2005 XML 11 Element Structure Principal element structure – –Start Tag –  Name of element  Zero or more attributes Each a name-value pair Uniquely named; Order insignificant –Content – possibly nested elements, and other things –End Tag -  Name – MUST be same name as in matching Start Tag Like HTML – but stricter – must have end tag …. Start tag End tag Content nameattributeAttribute: name-value pair

12. Enabling Grids for E-sciencE ISSGC’05 – June 2005 XML 12 Attributes A name-value pair that is included in the start tag of an element Name is part of specific language Value may also be part of a specific language – QName – qualified name More properly the above might be < BusinessForms:Invoice BusinessForms:customerType =“BusinessForms:trade” BusinessForms:dateStyle=“USnotations:date”> … This starts to get convoluted – necessary for designing for multi-lingual documents ….

13. Enabling Grids for E-sciencE ISSGC’05 – June 2005 XML 13 Empty Elements Empty Element Tags – Shorthand for element with no content just attributes perhaps indicated by / > not > Same as …. Start tag End tag Content Empty Element Tag

14. Enabling Grids for E-sciencE ISSGC’05 – June 2005 XML 14 Nested Elements Account and Items are child elements – –Non-unique names –Usually order is significant This is not a usual programming language configuration Best if each compound item is either –Structure (Struct) – uniquely named components –Array – multiple same-named components … … …

15. Enabling Grids for E-sciencE ISSGC’05 – June 2005 XML 15 Direct Character (Simple) Content 17.35 is an element with just character data –A simple value All simple values are text strings, but may have particular syntax and interpretation as decimal, integer, date, …. 10/24/04 17.35 10/29/04 2173.35

16. Enabling Grids for E-sciencE ISSGC’05 – June 2005 XML 16 Notation Will use XML a lot - Schemas, Soap messages, WSDLs – –so use clearer/briefer notations Textual – direct translation to actual XML Generally will use indentation to indicate structure Abbreviate End Tags to just Always have to actually put name in end tag !!!! Tree diagram – to emphasise structure 10/24/04 17.34 17-23-57 17.5 … 10/24/04 ….

17. Enabling Grids for E-sciencE ISSGC’05 – June 2005 XML 17 XML - NAMESPACE Structure  Philosophy  Detailed XML Format  Namespaces

18. Enabling Grids for E-sciencE ISSGC’05 – June 2005 XML 18 Namespaces A namespace (= “language”) –Defines a collection of names (a vocabulary)  For UK : {address, county, postCode, …. } –Usually has an associated syntax (e.g. Schema definition)  address = … county, postCode, …  Syntax may be available to S/W processing it –Implies a semantics – the (programmer writing) S/W processing a UK:address knows what it means –Provides a unique prefix for disambiguating names from different originators  UK vs. US vs. INT … … … … … … … … … … …. ….

19. Enabling Grids for E-sciencE ISSGC’05 – June 2005 XML 19 Namespace Names To get uniqueness of namespace name, use a URI –UK:postCode is really HTTP://www.UKstandards.org/Web/XMLForms:postCode (mythical) –The URI might be a real URL, for accessing the syntax definition, documentation, …. –But it may be just an identifier within the internet domain owned by the namespace owner

20. Enabling Grids for E-sciencE ISSGC’05 – June 2005 XML 20 Namespace Prefixes UK:postCode is really www.UKstandards.org/Web/XMLForms:postCode But HTTP://www.UKstandards.org/Web/XML/Forms:postCode is –Tediously long to use throughout the document –Outside XML name syntax  Namespaces are not part of XML  A supplementary standard http://www.w3.org/TR/REC-xml-nameshttp://www.w3.org/TR/REC-xml-names A W3C recommendation In an XML document –declare a namespace prefix, as an attribute of an element  xmlns:UK=“HTTP://www.UKstandards.org/Web/XML/Forms” –then use that for names in that namespace - UK:postCode  UK:post code is called a QName (qualified name)

21. Enabling Grids for E-sciencE ISSGC’05 – June 2005 XML 21 Namespace Prefix Declarations Namespace declaration occurs as an attribute of an element –i.e. within a start tag Scope is from beginning of that start tag to matching end tag –Excluding scope of nested re-declarations of same prefix Can declare a default namespace –xlmns=“www/3” – this is the name space for all un-qualified names in the scope of this declaration, eg. Street –But no defaulting for attributes – if no prefix, no namespace … … … … … … … … … … …. ….

22. Enabling Grids for E-sciencE ISSGC’05 – June 2005 XML 22 Well-formed and Valid Well-formed means it conforms to the XML syntax, e.g. –Start and end tags nest properly with matching names Valid means it conforms to the syntax defined by the namespaces used –Can’t check this without a definition of that syntax –  Normally a Schema  DTD (document Type Definitions) – deprecated  Others type definition system – some more sophisticated than Schemas

23. Enabling Grids for E-sciencE ISSGC’05 – June 2005 XML 23 THE END